In Season 8 Episode 23/24, Robin looks for the locket in Central Park. She think to ask Barney & Ted to come to Central Park. But she doesn't tell anyone that she is Central Park. How can Ted & Barney reach that location. I thought Robin didn't say that she was in Central Park
Keep in mind that this entire show is a flashback, representing the story that Ted is telling to his kids. There are many things shown in the show that are factually incorrect, including but not limited to: people eating sandwiches when they were really smoking weed, everyone in the group being smokers even though it isn't ever mentioned except in one episode, and Lily and Marshall literally communicating through telepathy and, on at least one occasion, passing plot-relevant information to one another by doing so.
What we see on screen is what Ted tells his kids, not a full and proper accounting of what really happened. The simplest explanation to your question is that Ted neglected to relate to his kids how he and Barney found out Robin was in Central Park.